The present invention relates to an apparatus and method for electron beam inspection with projection electron microscopy, the apparatus and method being intended to irradiate with a planar electron beam an object to be inspected (hereinafter, this object may be referred to as the object), and inspect defects or defect candidates present on the object.
During electron beam inspection of semiconductor wafers, electron beam inspection apparatuses of the projection electron microscopic type using a planar electron beam to irradiate an object to be inspected are used as powerful tools to improve throughput, instead of the scanning type that uses spot-shaped electron beam irradiation. These electron beam inspection apparatuses are known in Japanese Patent Laid-open Nos. 2003-202217 and 2004-363085, and in Japanese academic journal papers “Hasegawa et al.: Development of EB wafer Inspection Technique by Using Mirror Electron Projection, LSI Testing Symposium, pp. 89-93, 2004”, “Murakami et al.: Development of an Electron Beam Inspection System Based on Projection Imaging microscopy, LSI Testing Symposium, pp. 85-87, 2004”, “Nagahama et al.: Inspection performance of the electron beam inspection system based on projection electron microscopy, pp. 921-928, SPIE Vol. 5375, 2004”, and “Satake et al.: Electron beam inspection system for semiconductor wafer, based on projection electron microscopy, pp. 1125-1134, SPIE Vol. 5375, 2004”.
Japanese Patent Laid-open No. 2003-202217 describes a defect inspection apparatus that detects the existence and positions of defects in a plurality of regions on the surface of an object to be inspected (hereinafter, this object is referred to as the object). Defect detection by this apparatus includes: forming an electric field that decelerates an electron beam, on the surface of the object; reflecting, in the immediate vicinity of the surface of the object, a planar electron beam that includes energy components unable to reach the surface of the object because of the presence of the deceleration electric field and has a certain area, and forming images of the plural regions of the surface of the object by use of an image-forming lens; acquiring the images; storing the acquired images into an image storage section; and detecting the existence and positions of defects in the plural regions by comparing the stored images.
Also, Japanese Patent Laid-open No. 2004-363085 describes an inspection apparatus including: electron irradiating means that creates a crossover by generating an electron and forming images at a desired magnification, and irradiates a substrate with the electron so as to form a desired sectional shape; means that moves at least either one of the electron with which the substrate is to be irradiated, and a stage to hold the substrate, and moves, in a relative fashion with respect to the electron or the stage, the regions on the substrate that are to be irradiated with charged particles; a detector that detects the electron which has been used to obtain information on the surface of the substrate; means that acquires a detection image of a die to be inspected, by using the information of the substrate surface which has been detected by the detector; means that acquires an image of a reference die which is used as the basis for comparison with the detection image of the die to be inspected; and means that compares the image of the reference die and the image of the die to be inspected.
However, neither of the above six publications has given any consideration to an automatic focusing technique for conducting real-time corrections for changes in focus offsets due to time-varying changes in the electrically charged state of the surface of the object, in the respective electron beam inspection techniques based on projection electron (or imaging) microscopy. That is, no such consideration has been given in Japanese Patent Laid-open Nos. 2003-202217 and 2004-363085 or in Japanese academic journal papers “Hasegawa et al.: Development of the wafer electron beam inspection technology based on mirror electron projection, LSI Testing Symposium, 2004”, “Murakami et al.: Development of an electron beam defect inspection system based on projection imaging microscopy, LSI Testing Symposium, pp. 85-87, 2004”, “Nagahama et al.: Inspection performance of the electron beam inspection system based on projection electron microscopy, pp. 921-928, SPIE Vol. 5375, 2004”, and “Satake et al.: Electron beam inspection system for semiconductor wafer, based on projection electron microscopy, pp. 1125-1134, SPIE Vol. 5375, 2004”.